Method for adaptively controlling knocking of a gasoline direct fuel injection internal combustion engine, and a corresponding device

ABSTRACT

A method of adaptive knock control and a corresponding device for a direct-gasoline-injection internal combustion engine are described, the internal combustion engine being operated in at least two operating modes, the at least two operating modes differing by the status of at least one operating variable and/or at least one basic model concept. For knock control, relevant retardation angles of the firing angle are calculated by using an adaptable computation specification or they are stored in the adaptive engine characteristics map and read out of the adaptive engine characteristics map, the adaptive engine characteristics map being subdivided into ranges for at least one operating parameter, a retardation angle being assigned to each range. For the at least two operating modes, a separate adaptive engine characteristics map or a separate adaptable computation specification is provided, and when the operating mode changes, the instantaneous retardation angle is read out of the adaptive engine characteristics map of the new operating mode or is calculated by using the new adaptable computation specification.

FIELD OF THE INVENTION

The present invention is directed to a method of adaptive knock controlof an internal combustion engine and a corresponding device forperforming the method of adaptive knock control.

BACKGROUND INFORMATION

There are already known internal combustion engines that operate withdirect gasoline injection. For operation of these internal combustionengines, a distinction is made between operating modes such ashomogeneous operation and stratified charge operation or homogeneouslean operation. In addition, a method and a corresponding device foradaptive knock control are known from published German PatentApplication 195 32 504, where relevant firing angle retardation anglesfor knock control are stored in an adaptive engine characteristics mapupon leaving an adaptive engine characteristics map range and are readout of the adaptive engine characteristics map under certain conditions.For the load operating parameter or the rotational speed operatingparameter, the adaptive engine characteristics map is subdivided intoranges, each of which is assigned a firing angle retardation angle.

SUMMARY

According an embodiment of the present invention an overwriting of theretardation angle of the adaptive engine characteristics map occursduring a change in operating modes and, due to the fact that theretardation values are read out of the specific engine characteristicsmap, the occurrence of unnecessary knocking or excessive retardation isprevented.

Six operating modes are currently differentiated and may also bedifferentiated to advantage with respect to adaptive knock control. Inaddition, the load and/or the rotational speed are selected as operatingparameters on which the adaptive engine characteristics map valuesdepend, because the firing angle and thus also the retardation angle areinfluenced primarily by these parameters. The adaptive enginecharacteristics maps are individually provided for each cylinder.

DETAILED DESCRIPTION

Knocking, i.e., an abnormal combustion process in the combustion chamberof an internal combustion engine, limits the power and efficiency andresults in damage to the combustion chamber due to the high flamespeeds. To prevent this, systems for knock detection and knock controlare integrated into modern engines. Such systems are adequately wellknown from the literature, so their functioning will only be summarizedbriefly below.

Signals from the combustion chamber are detected by knock sensorsbelonging to the knock detection system and are relayed to an analyzingunit which also belongs to the knock detection system. Such signals maybe, for example, acoustic signals, electromagnetic signals, electricsignals, pressure signals, or temperature signals picked up by the knocksensors inside or outside of the combustion chamber. The analyzing unitamplifies the signals and integrates them in a suitable manner, so thatafter an analog/digital conversion of the signals, the integrated valuemay be compared with a threshold value in a microprocessor in theengine, knocking being detected when the threshold value is exceeded.For example, a selection of a certain frequency band and/or a selectionwith respect to a certain time window is also made in the analyzing unitto suppress interference signals, the frequency band and/or the timewindow being characteristic of the occurrence of knocking signals.

If knocking has been detected, knock control is performed by themicroprocessor integrated into the engine in such a way that aretardation angle is added to a fundamental firing angle, the sumforming the basic firing angle. The retardation angle is defined as apositive value in the sense of the present invention. A torque-basedfiring angle representing the earliest possible firing angle iscalculated from the torque structure on the basis of the torquerequirements. The basic firing angle and the torque-based firing angleare then compared in the method of calculating the firing angle, usingthe later of the two firing angles, i.e., the firing angle closer to topdead center (TDC) as the firing angle to be implemented. The fundamentalfiring angle is read out of a load-dependent and/or rotationalspeed-dependent engine characteristics map which contains firing anglesunder normal conditions and is stored in the microprocessor of theengine. It contains values for fundamental firing angles assigned tocertain rotational speed ranges and/or load ranges. The rotational speedis determined by sensors which are preferably mounted on the crankshaft.The load, i.e., the relative air filling of the particular cylinder, isdetermined by the microprocessor on the basis of various operatingparameters such as the rotational speed, torque demand and the measuredvalues of the hot-film air-mass meter (HFM) and the intake manifoldpressure sensor, the rate of recycled exhaust gas or the position of thethrottle valve with the help of models and is made available for thedetermination of the fundamental firing angle. The relative air fillingis defined as the ratio of the instantaneous air filling and the airfilling under normal conditions for the particular cylinder. The firingangle is retarded due to the knock control until no more knockingoccurs. The adjustment of the firing angle in the individual steps isadded to a retardation angle which indicates the total adjustment of thefiring angle based on the fundamental firing angle. If no knockingoccurs over a certain period of time, then the firing angle is advancedagain by the knock control system, i.e., the firing angle is atcrankshaft angles farther before TDC. Accordingly, the retardation angleis reduced because of the firing angle having been advanced.

Adaptive knock control provides that the retardation angles are storedin an adaptive engine characteristics map, which is subdivided intovarious ranges for at least one operating parameter, or they are readout of this adaptive engine characteristics map. The adaptive enginecharacteristics map is stored in the microprocessor, which also controlsthe reading and storing of the retardation angles. An instantaneousretardation angle is preferably stored on leaving a range of theadaptive engine characteristics map when the instantaneous retardationangle is later by a certain applicable angle than the retardation anglestored previously for the range just departed. An earlier instantaneousretardation angle, in comparison with the retardation angle storedpreviously, may also be stored in the particular engine characteristicsmap range likewise on leaving a range of the adaptive enginecharacteristics map on the condition that the instantaneous retardationangle has already been used over a certain period of time. Under certainconditions, e.g., when switching to knock control with the adaptiveengine characteristics map, the corresponding retardation angle is readout of the range of the adaptive engine characteristics map whichincludes the at least one instantaneous operating parameter. Likewise, aretardation angle is read out of the adaptive engine characteristics mapwhen the value of at least one instantaneous operating parameter changesso that it falls in another range of the adaptive engine characteristicsmap. Then the retardation angle is read out of the other range of theadaptive engine characteristics map. In another exemplary embodiment,the retardation angle is read out of the other range of the adaptiveengine characteristics map only when there is a dynamic change in atleast one operating parameter, i.e., when the change in the at least oneoperating parameter in a certain period of time exceeds a certainapplicable threshold value. The retardation angle read out of theadaptive engine characteristics map is used as the new instantaneousretardation angle in all the examples described.

There are already known engines having direct gasoline injection,whereby different operating modes are differentiated for the operationof such engines. Operating modes are operating states characterized bythe status of important operating variables and/or basic model concepts.Within one mode of operation, the states of the operating variables arethen variable only within certain limits. Important operating variablesinclude, for example, the point in time of the injection, the number ofinjection operations, the quantity of fuel to be injected and thus alsothe fuel/air ratio λ, the firing angle retardation, or the firing angle.Basic model concepts may include the torque model or other models ofnonmeasurable variables that may be used to calculate all the operatingvariables. The use of a certain model may be initiated, for example,independently of other parameters, e.g., when certain nonmeasurableexternal conditions are in effect. In another exemplary embodiment, theuse of a certain model, e.g., for the torque or the processes in theintake manifold, may be initiated by the microprocessor if certainrequirements exist and/or operating variables have certain values. Forexample, at high rotational speeds, use of the torque model for ahomogeneous mixture having a fuel/air ratio of almost 1 prevailing inthe combustion chamber forms the basis for the calculations when a highacceleration is also required due to the position of the gas pedal. Ifthe rotational speeds are low and the dynamic power desired through theposition of the gas pedal is low, a different torque model which iscorrect for a stratified mixture in the combustion chamber, for example,is used as the basis for calculation.

The following operating modes are differentiated and controlled by themicroprocessor: homogeneous, homogeneous lean, stratified charge,homogeneous stratified charge, homogeneous antiknock, andstratified-charge catalytic converter heating. However, the inventionpresented here is not limited to the operating modes listed here, andthe method and/or device may also be used similarly for other operatingmodes.

The following description of the operating modes is based on afour-stroke method, which is used predominantly fordirect-gasoline-injection internal combustion engines. The four strokesare known as the intake stroke, the compression stroke, the working orcombustion stroke, and the exhaust stroke, in that order.

In the homogeneous operating mode, fuel is injected once into thecombustion chamber in the intake stroke, the amount of fuel injectedbeing metered so the fuel/air ratio λ is approx. 1. Fuel mixes with theair in the combustion chamber so that there is a uniform distribution offuel. In this operating mode, a torque model different from the otheroperating modes mentioned here is used.

The homogeneous lean operating mode is the operating mode in which thefuel distribution in the combustion chamber is also uniform, but thefuel/air ratio achieved is significantly greater than 1.

This is achieved by injecting a much smaller amount of fuel into thecombustion chamber in comparison with the homogeneous operating mode.Fuel is again injected once in the intake stroke.

In the stratified-charge operating mode, fuel is injected into thecombustion chamber so late, i.e., in the compression stroke, that thereis no longer a uniform distribution of, fuel. Thus, there is anignitable cloud of fuel mixture only in proximity to the spark plug,i.e., there is: a stratified distribution of the fuel-air mixture.

The homogeneous stratified-charge operating mode is the operating modein which fuel is injected in both the intake stroke and the compressionstroke. With the first injection, a lean basic mixture distributeduniformly in the combustion chamber is produced, in which a rich, highlyflammable stratified-charge cloud is deposited near the spark plugduring the second injection. The flame produced by the rich mixture isable to spread into the lean basic mixture, so that it is also convertedcompletely.

In the homogeneous antiknock operating mode, as in the homogeneousstratified charge operating mode, fuel is injected in the intake strokeand in the compression stroke, but the antiknock operating mode is usedwhen the retardation angle of the firing angle achieved because ofknocking has become too large and thus the loss of torque due to thelarge retardation angle has also become too great. The homogeneousantiknock operating mode achieves a reduction in the knocking tendencyof the fuel/air mixture in the combustion chamber due to the coolingeffect of the fuel injected later and due to the lean areas at theedges, so it is possible to reduce the retardation of the firing anglebrought about by the knocking. This permits an improvement inefficiency.

The stratified charge catalytic converter heating operating mode is theoperating mode in which fuel is injected into the combustion chamber inboth the compression stroke and the combustion stroke. In particular thefuel injected in the second injection cycle is very late in burning andthus greatly heats up the exhaust gas line. Therefore, various parts ofthe catalytic converter quickly reach their operating temperature.

A first exemplary embodiment of the method and the device according tothe present invention provides that different adaptive enginecharacteristics maps are stored in the microprocessor of the internalcombustion engine for at least two of the operating modes mentionedabove. The adaptive engine characteristics maps may differ in the valuesstored in the individual ranges of the adaptive engine characteristicsmap and in a different division and/or size of the ranges of the enginecharacteristics maps. For example, there is a first adaptive enginecharacteristics map for the homogeneous operating mode and a secondadaptive engine characteristics map for the homogeneous lean operatingmode. As it is possible to operate in the homogeneous operating mode inall load ranges and/or rotational speed ranges, the first adaptiveengine characteristics map contains all the load ranges and/orrotational speed ranges. For example, the loads that occur are dividedinto four ranges and the rotational speeds that occur are divided intosix ranges, so the resulting first adaptive engine characteristics maphas 24 engine characteristics map ranges. The homogeneous lean operatingmode, however, is used only at low loads and rotational speeds; forexample, the second adaptive engine characteristics map includes onlytwo load ranges, so that the second adaptive engine characteristics maphas a total of 12 ranges which may also differ in size from the size ofthe adaptive engine characteristics maps of the first adaptive enginecharacteristics map. In another exemplary embodiment, the number ofrotational speed ranges could also be modified, so the second adaptiveengine characteristics map would include two load ranges and threerotational speed ranges, for example, which would yield a total of sixranges for the second adaptive engine characteristics map.

If the microprocessor changes the operating mode, e.g., from homogeneouslean to homogeneous because of a change in the torque demand, a higherrotational speed, a change in dynamics, etc., then in the device and/orthe method according to the present invention, the instantaneousretardation value for determining the basic firing angle is read out ofthe first adaptive engine characteristics map for the new, operatingmode. The retardation value is read out of the range of the firstadaptive engine characteristics map which corresponds to theinstantaneous load and the instantaneous rotational speed. Theretardation value achieved in the homogeneous lean operating mode is notused. Accordingly, in switching to another operating mode, theretardation value is read out of the range of the adaptive enginecharacteristics map of the other operating mode which corresponds to theinstantaneous operating parameters.

In another exemplary embodiment of the present invention, the adaptiveengine characteristics maps are provided on an individual basis for eachcylinder, so there is a separate adaptive engine characteristics map foreach cylinder and each operating mode. Thus, the given facts for eachindividual cylinder may be taken into account optimally. The particularinstantaneous cylinder is determined with the help of camshaft sensorsand/or crankshaft sensors, and the cylinder identification contained inthe microprocessor is determined.

In another exemplary embodiment of the present invention, instead of anadaptive engine characteristics map, a computation specification mayalso be made available for each operating mode so that the retardationangle may be calculated. The calculation is performed by themicroprocessor of the internal combustion engine. The computationspecification may be adapted, for example, by adapting the parameters ofthe particular computation specification used as a function of theinstantaneous retardation angles. Like the adaptive enginecharacteristics map, the computation specification depends on operatingparameters such as the load and/or rotational speed. In anotherexemplary embodiment, as in the above exemplary embodiment, thecomputation specification of the new operating mode is used to calculatethe retardation angle after a change from an old operating mode to a newoperating mode. In another exemplary embodiment, the computationspecification may additionally be implemented individually for eachcylinder in the microprocessor of the internal combustion engine.

Providing different adaptive engine characteristics maps or computationspecifications for different operating modes ensures that for eachoperating mode there is an adaptive engine characteristics map adaptedto the corresponding conditions, so it is possible to minimize thenumber of overwrite operations. In addition, unnecessary knocking isprevented, because the “correct” retardation value may always be setalready when there is a change in operating mode.

What is claimed is:
 1. A method of adaptive knock control of adirect-gasoline-injection internal-combustion engine, comprising:operating the engine in at least two of homogeneous operating mode,homogeneous lean operating mode, stratified-charge operating mode,homogeneous stratified-charge operating mode, homogeneous antiknockoperating mode, and catalytic converter heating operating mode, wherein;in the homogeneous operating mode, fuel is injected once into acombustion chamber in an intake stroke, an amount of fuel injected beingmetered so that the fuel/air ratio λ is approximately 1; in thehomogeneous lean operating mode, fuel is injected once into a combustionchamber in an intake stroke, an amount of fuel injected being metered sothat the fuel/air ratio achieved is significantly greater than 1; in thehomogeneous stratified-charge operating mode, fuel is injected into thecombustion chamber in a compression stroke so that there is no uniformdistribution of fuel; in the homogeneous stratified-charge operatingmode, fuel is injected in both the intake stroke and the compressionstroke, so that with a first injection a lean basic mixture distributeduniformly in the combustion chamber is produced, and during a secondinjection a rich, highly flammable stratified-charge cloud is depositednear a spark plug; in the homogeneous antiknock operating mode, fuel isinjected in the intake stroke and in the compression stroke, and aretardation angle of a firing angle achieved because of knocking hasexceeded a predetermined threshold; in the catalytic converter heatingoperating mode, fuel is injected into the combustion chamber in both thecompression stroke and a combustion stroke; determining a retardationangle of a firing angle for knock control using one of an adaptablecomputation specification and an adaptive engine characteristics map,the adaptive characteristics map being subdivided into a plurality ofranges for at least one operating parameter, each of the plurality ofranges being assigned with a corresponding retardation angle, whereinone of a separate, dedicated adaptive engine characteristics map and aseparate, dedicated adaptable computation specification is provided foreach of the at least two operating modes; performing, in response to achange in the operating mode to a new operating mode, one of reading aninstantaneous retardation angle from a corresponding adaptive enginecharacteristics map for the new operating mode and calculating aninstantaneous retardation angle using a corresponding adaptivecomputation specification for the new operating mode; and one of storingretardation angles in the corresponding adaptive engine characteristicsmap and adapting the corresponding adaptive computation specification asa function of knocking of the internal combustion engine.
 2. The methodaccording to claim 1, wherein at least one of the adaptive enginecharacteristics maps and the adaptable computation specifications forthe at least two operating modes is further differentiated according toindividual cylinders of the internal combustion engine.
 3. The methodaccording to claim 1, wherein an instantaneous retardation angle isstored upon exceeding a range of the corresponding adaptation enginecharacteristics map, if the instantaneous retardation angle is later bya predetermined angle than a retardation angle stored previously for therange that has been exceeded.
 4. The method of claim 1, wherein aninstantaneous retardation angle that is earlier in comparison with aretardation angle stored previously is stored, if the instantaneousretardation angle has already been used over a predetermined period oftime.
 5. A device for adaptive knock control of adirect-gasoline-injection internal-combustion engine, comprising: anarrangement for controlling the engine operating in at least two ofhomogeneous operating mode, homogeneous lean operating mode,stratified-charge operating mode, homogeneous stratified-chargeoperating mode, homogeneous antiknock operating mode, and catalyticconverter heating operating mode, wherein; in the homogeneous operatingmode, fuel is injected once into a combustion chamber in an intakestroke, an amount of fuel injected being metered so that the fuel/airratio λ is approximately 1; in the homogeneous lean operating mode, fuelis injected once into a combustion chamber in an intake stroke, anamount of fuel injected being metered so that the fuel/air ratioachieved is significantly greater than 1; in the homogeneousstratified-charge operating mode, fuel is injected into the combustionchamber in a compression stroke so that there is no uniform distributionof fuel; in the homogeneous stratified-charge operating mode, fuel isinjected in both the intake stroke and the compression stroke, so thatwith a first injection a lean basic mixture distributed uniformly in thecombustion chamber is produced, and during a second injection a rich,highly flammable stratified-charge cloud is deposited near a spark plug;in the homogeneous antiknock operating mode, fuel is injected in theintake stroke and in the compression stroke, and a retardation angle ofa firing angle achieved because of knocking has exceeded a predeterminedthreshold; in the catalytic converter heating operating mode, fuel isinjected into the combustion chamber in both the compression stroke anda combustion stroke; an arrangement for determining a retardation angleof a firing angle for knock control using one of an adaptablecomputation specification and an adaptive engine characteristics map,the adaptive characteristics map being subdivided into a plurality ofranges for at least one operating parameter, each of the plurality ofranges being assigned with a corresponding retardation angle, whereinone of a separate, dedicated adaptive engine characteristics map and aseparate, dedicated adaptable computation specification is provided foreach of the at least two operating modes; an arrangement for performing,in response to a change in the operating mode to a new operating mode,one of reading an instantaneous retardation angle from a correspondingadaptive engine characteristics map for the new operating mode andcalculating an instantaneous retardation angle using a correspondingadaptive computation specification for the new operating mode; and anarrangement for one of storing retardation angles in the correspondingadaptive engine characteristics map and adapting the correspondingadaptive computation specification as a function of knocking of theinternal combustion engine.
 6. The device according to claim 5, whereinat least one of the adaptive engine characteristics maps and theadaptable computation specifications for the at least two operatingmodes is further differentiated according to individual cylinders of theinternal combustion engine.
 7. The device according to claim 5, whereinan instantaneous retardation angle is stored upon exceeding a range ofthe corresponding adaptation engine characteristics map, if theinstantaneous retardation angle is later by a predetermined angle than aretardation angle stored previously for the range that has beenexceeded.
 8. The device according to claim 5, wherein an instantaneousretardation angle that is earlier in comparison with a retardation anglestored previously is stored, if the instantaneous retardation angle hasalready been used over a predetermined period of time.